The present invention relates to a valve control system for controlling the engine poppet valves of an internal combustion engine, and more particularly, to a valve control system of the valve deactivation type.
Although the valve control system of the present invention may be utilized to introduce some additional lash into the engine poppet valve train, such that the valves open and close by an amount less than the normal opening and closing, the invention is especially well suited for introducing into the valve train sufficient lash (also referred to hereinafter as “lost motion”), such that the valves no longer open and close at all, and the invention will be described in connection therewith. Vehicle manufacturers wish to be able to incorporate into their engines such valve deactivation capability so that, for example, under light engine load conditions, several of the engine intake poppet valves may be deactivated, thus improving the fuel economy of the vehicle.
Although the valve control system of the present invention may be utilized in various types and configurations of valve gear train, it is especially well suited for use in a valve gear train of the “end pivot rocker arm” type, and will be described in connection therewith by way of example only, and not by way of limitation. In an end pivot rocker arm type of valve gear train, the so-called “end pivot” typically comprises the ball plunger portion of a hydraulic lash adjuster (also referred to hereinafter as an “HLA” or as a “lash compensation device”). A rocker arm has one end thereof pivotally mounted on the ball plunger portion of the HLA, and the opposite end in engagement with the stem tip of the engine poppet valve. Intermediate these opposite ends, the rocker arm includes a cam follower portion in engagement with the cam lobe of a camshaft, all of which is now well known to those skilled in the engine valve train art.
It is also now well known to those skilled in the art to provide valve control systems of the type including “valve deactivation” capability. In one known embodiment of a valve deactivation control system, for an end pivot rocker arm valve gear train, there is provided a hydraulic lash adjuster which includes a moveable latch member. By way of example only, the latch member would typically be operably associated with the cylinder head bore within which the HLA is disposed and with an axially moveable body member of the HLA. Thus, the HLA may be operated in either: (i) a latched condition, in which case the rotation of the camshaft would result in normal valve lift, or (ii) an unlatched condition, introducing lost motion into the valve gear train, whereby rotation of the camshaft would result in very little lift, or more commonly, no lift at all of the respective engine poppet valve.
Such valve deactivation control systems have now started to enjoy a certain amount of commercial success, although the required latching mechanism, and the associated controls, add substantially to the overall cost of the engine valve train. More significantly, the typical prior art valve deactivation system requires a lost motion spring (required to bias the “unlatched” portion of the HLA back toward its normal, latched position). As is well known in the art of such systems, the lost motion in the valve gear train is typically about equal to the maximum valve “lift” (i.e., the linear movement of the engine poppet valve as it opens), thus indicating the size and travel of the required lost motion spring. In addition to the extra expense of providing such a lost motion spring, the presence of a deactivating type of HLA requires substantially more space within the cylinder head, thus complicating the packaging of the overall valve train system.
If the required lost motion spring for use in a deactivating type HLA could be a very small, low force spring, the additional cost of the lost motion spring and the packaging of the deactivating HLA would not comprise a deterrent to the commercialization of such valve deactivation systems. However, as will be understood by those skilled in the art, the lost motion spring must typically be sized (in terms of bias force) such that the lost motion spring will be able to maintain the dynamic stability of the valve gear train, whenever it is operating in the “valve deactivated mode”.